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Foes of GE salmon raise specter of 'Trojan gene' effect

November 26, 2010 | 1:49
pm

The Food and Drug Administration's public comment period for labeling requirements for a genetically engineered salmon ended not so quietly, with a flurry of press releases leading up to Monday’s deadline.

They included an announcement by a group of lawmakers from Alaska and the Northwest that would prohibit FDA approval of a GE salmon, or require that it be labeled as genetically engineered in the event regulators approved the fish.

A key element of the last-minute volley was a letter from a dozen environmental, science and consumer groups to FDA Commissioner Margaret Hamburg urging her to look carefully at possible adverse ecological consequences as it evaluates a Massachusetts firm’s application for a GE salmon for human consumption. If approved, the salmon would be the first GE food animal.

“We anticipate that a comprehensive [review] will show that the [GE] salmon pose a threat to wild salmon populations and the health of marine and freshwater ecosystems around the world,” the letter states.

The AquaBounty Technologies’ AquaAdvantage salmon reaches market weight in about half the time of a regular North Atlantic salmon.

The letter reminds the FDA of the need to consider a worst-case scenario: that the GE salmon, which is to be raised in closed, land-based facilities, will escape and inflict unknown consequences on the environment.

It leans heavily on perhaps the most hotly disputed evidence in the GE salmon debate, the so-called Trojan Gene effect, in which a specific genetic advantage -– in this case the AquaBounty salmon’s ability to grow faster -- enables it to outcompete unaltered salmon, leading to their demise.

The letter states: "If salmon genetically engineered to grow faster than wild fish escape confinement, they will threaten the health and survival of wild salmon populations. According to research from Purdue University, if just 60 GE fish were released into a wild population of 60,000, the wild population could be extinct within 40 generations. This result is driven by the “Trojan gene effect” in which specific fitness advantages in an otherwise less fit organism result in gene spread and an ultimate weakening and eventual collapse of the species.

Not so, says the author of the Trojan Gene hypothesis, William Muir, an animal science professor at Purdue who has been yelling loudly, to little effect so far, that his work is being misrepresented by the GE salmon’s opponents.

Muir said the assumption at the time of the study in 1999 was that a GE salmon would grow faster and bigger and that its size would be an unbeatable advantage in mating.

But AquaBounty salmon don’t get any bigger than ordinary salmon, they just reach full size faster, so any size advantage they have is temporary.

More importantly, Muir said that studies show that transgenic salmon are lousy at the courtship required for mating.

On Sept. 20, Muir told the FDA Veterinary Medicine Advisory Committee evaluating the GE salmon that “the data conclusively shows that there is no Trojan Gene effect as expected. The data in fact suggest that the transgene will be purged by natural selection. In other words the risk of harm here is low.”

In an e-mail to Greenspace, Muir said that “the concept of a Trojan Gene entering a population due to mating advantage is now known to be an urban myth. The myth is that females like males who are larger. In fact, females like males who have good courtship displays. Who would have thought the jocks would loose out to the nerds when it came to attracting girls!! Thus because the fish grows faster does not automatically result in the Trojan Gene. It is like saying ‘If the sun were to nova all the people of the earth would be killed,’ but then reporting that scientist says ‘the sun will kill all the people of the earth’ The sin of omission is as great as the sin of insertion.”

Muir notes that his own research states that “with nearly continuous access to females, [GE] males courted them frequently; however, the vast majority of courtship attempts ended in female rejection displays.”

There’s no indication of when the FDA, which has been mulling the GE salmon for more than a decade, will make a decision, though the agency’s has made a preliminary determination that the fish is safe for people to eat and does not pose a significant environmental risk.

The FDA’s veterinary advisory committee in September recommended further study of the fish’s potential to trigger allergies or other health problems in some consumers.

While the panel did not make a recommendation either to approve or reject the fish, comments and questions seemed to convey a sense that the fish is safe for human consumption, though several panelists expressed concern about the small sample sizes of some studies.

Photo: AquAdvantage salmon would be the first gene-altered animal sold for food. This handout photo, released Aug. 30, 2010, compares the size of its genetically engineered AquAdvantage Salmon (background) with an Atlantic salmon of the same age (foreground). Credit: Reuters/Barrett & McKay/AquaBounty Technologies